In recent years, consumer products such as cultured dairy products (typified by cottage cheese, sour cream, dips and yogurt), prepared meat (typified by chicken livers and ground ham) and delicatessen products (typified by potato salad and oil-cured black olives) have come to be packaged in differential pressure-thermoformed, lidded containers, as have a great number of other food and non-food items. Most typically, the cup-portions and lid-portions of these containers are differential pressure-thermoformed from initially uniform-thickness thermoplastic sheeting, most often made of polystyrene. Although the lids and cups may be formed from sheeting which is equal in thickness with one another, it is not uncommon for one thickness of sheeting to be used in making the cups and another thickness of sheeting to be used in making the lids. And even in instances where the sheeting may originally have been of the same thickness, differences in drawing depth into a die cavity may cause, and usually does cause, various regions of the walls of the lids and cups to be of thicknesses which, while highly uniform from one cup to the next and from one lid to the next, are different from one another.
For illustrative purposes, a twenty-four ounce differential pressure-thermoformed lidded polystyrene container for cottage cheese may be selected as typical of the container to which the present invention is addressed as an improvement. Looking in 1987, in the United States, at the typical package of this type which is widely marketed, one notices a number of factors. The lidded container is made of thin, stiffly flexible material. Particularly the middle portion of the cup sidewall has some "give" to it, although its lower corner is stiff enough to resist denting in normal filling, supply, carrying home from the grocery and in holding while scooping out the product. So, too, at the interfacial ring where the lid removably sealingly stops the mouth of the cup, the material is sufficiently stiff and resilient that there is an interference fit which helps hold the lid in place; a significant, but readily manually-supplied force must be applied to intentionally pluck or extract the lid from the container, but in the normal supplying and carrying home of the filled, lidded container, neither the cup nor the lid usually distorts sufficiently to cause the lid/cup seal to be broken or the lid to come off. The typical conventional such lidded container is very inexpensive and contributes little to the total cost of even a small quantity of a modestly priced consumer product (such as sixteen ounces of cottage cheese); so little, in fact, that the consumer is most apt to treat the conventional lidded container as a disposable item, or as a "free" reuseable container for leftovers, to use once more in the packing of lunches and the like.
Part of the low cost nature of such containers stems from the fact that manufacturing of them may be done on a large scale, because so many products of so many manufacturers are packaged in virtually the same such containers, but for surface graphics.
But, as a result, the containers often are made in plants that are geographically as well as financially separated from where the cups will be filled and lidded. Accordingly, another part of the success of such a container is that its parts must be able to be exteriorly printable on available machinery, preferably without more than minor modifications or adjustments; must be deeply nestable for cost-efficient boxing and shipping; and preferably are de-nestable, fillable and closable and conveyable on equipment that is already installed in the packer's plant, preferably without more than minor modifications or adjustments.
One might profitably consider at this juncture why, if such a proven, worthwhile, de-bugged product is so widely, conveniently and inexpensively available, would anyone want to go beyond what is conventional and to propose that changes be made.
An answer may be found in contemplating the highly publicized instances of consumer product tampering in the late 1970's - early 1980's, e.g. Tylenol: some manufacturers and packers of conventional lidded containers for cottage cheese and the like began to become concerned with whether, at least in some instances, these conventional lidded containers could be elaborated upon or, modified so as to make them tamper-proof, or if not tamper-proof, then at least provided with a readily tamper-evident feature.
One solution which appeared is the provision of an inner seal, i.e. a membrane which is sealed across the mouth of the filled cup under and independently of the lid. However, such a feature adds structure, expense, weight and processing steps to the packaged product and so is of limited acceptability. Also, it may require a substantial further investment in equipment at the packer level, not be feasible for use with a wide variety of container fillings, and indeed, be of limited acceptability as either a tamper-proofing or tamper-evidencing feature, because the consumer usually must remove the container lid in order to inspect whether the inner seal remains intact. Also, it may not always be easy to notice whether a portion of the edge of the inner seal has been pulled-away from the cup mouth rim.
To the knowledge of the present inventors, others have designed tamper-evidencing features into somewhat similar (e.g. sometimes competitive) injection molded lidded containers. However, there, the solutions are different in that they rely on making mold modifications which can provide lugs, protuberances, perforations and the like, solutions which are not feasible to build into a product which is to be differential pressure-thermoformed from uniform thickness synthetic plastic resin sheeting, e.g. made of polystyrene.
A sheet of polystyrene which has been extruded, like some other webs, usually retains in its physical structure artifacts of the direction of its extrusion. For instance, a newspaper can be ripped along a fairly straight line if one rips lengthwise of the paper web from which the newspaper was manufactured, but is much more difficult, in fact nearly impossible, to rip straightly crosswise of the web. Heretofore, the fact that polystyrene sheet cannot be ripped uniformly in all directions seems to have left other proposals for mass manufacturing two-piece tamper-evident lidded containers mere paper proposals, without a way of being commercially realized, despite the strongly-felt need.
In order to avoid being left without a product to satisfy the tamper-evident lidded container market, manufacturers of differential pressure-thermoformed containers made of polystyrene sheet have attempted other measures, in addition to the internal mouth-blocking barrier diaphragm mentioned above. One of these ways is to provide for the juncture between the cup and the lid an externally encircling band made of a heat-shrinkable material. On a filling line, using such an expedient requires the use of trays or the like for holding the lidded containers and the bands at the correct height relative to the cup/lid juncture until the assembly has passed through the shrink tunnel. Others have completely shrink-wrapped the lidded container with a layer of clear-plastic sheet. The added cost of wholly or partly shrink-wrapping a lidded container can easily amount to one hundred thousand dollars per packaging line, and the added cost of supplies for the third part of the package and for operating the line can easily run to 7 to 8 dollars per thousand containers.
The present inventors, together with their colleague, Gerald Burnett, in the 1983-1984 time period, devised what they believe to be the first technically feasible snap-together lidded cup made of differential pressure-thermoformed, generally uniform thickness synthetic plastic resin sheeting, e.g. made of polystyrene.
In that development, a container was provided in the form of a cup or container body with a round mouth removably closed by a lid, both differential pressure-thermoformed of stiffly flexible synthetic plastic resin sheeting, such as polystyrene. For providing a tamper-evidencing feature, the sidewall of the cup, adjacent the mouth, was integrally, circumferentially provided with an axially and radially surrounding guard flange. This flange was located at such a close proximity to the outer profile of the lid, when the lid is fully seated following filling of the cup with a product such as cottage cheese, that the consumer's fingers virtually cannot get at the lid or get between the lid and the cup to pluck or pry off the lid, nor can the user's fingers get under the outer edge of the lid to remove the lid from the cup. The guard flange was provided at two adjacent sites with radially directed notches or other lines of weakness defining between them a tab. Accordingly, the lid was designed to be removed from the cup by first pressing down on the guard flange tab defined between the two lines of weakness, thus splitting the guard flange along these two radially directed lines. Deformation was planned to be such that the tab then angles downwards at an angle that permits the user to get a finger between the tab and lid, under the outer periphery of the lid, so that the lid may be lifted up and removed. However, the deformation was also planned to be such as to give a conspicuous indication that the container lid has once been removed after the container was filled and lidded. The container was proposed to be filled and closed on largely if not wholly the same equipment as is widely in use at dairies, food processors and similar packers.
While that tamper-evident container reached a development and testing stage, it was never commercialized. That was principally because then-current U.S. Food and Drug Administration guidelines or regulations relating to containers for retailing packaged foodstuffs such as cottage cheese to consumers required that the mouth rim of the cup portion of the container be covered by a radially outer flange part of the lid, rather than vice versa, so that any debris which might have accumulated in that region between the time when the cup was lidded and the time when the lid was removed by the consumer would come off with the lid, rather than become free to fall from the cup rim region into the food in the unlidded cup. Thus, while that product was believed to be technically feasible, for governmental regulatory reasons it was not deemed to be a suitable answer to tamper-proofing or rendering tamper-evident consumer packages of cottage cheese and the like. It is believed to remain a suitable response to providing tamper-evident packaging for non-food products, and for food products if and where not governed by the abovementioned packaging regulations.
Accordingly, the present invention grew out of a desire to provide snap-together lidded cups made of differential pressure-thermoformed plastic resin sheeting, which made use of some of the principles learned as the aforementioned prior invention of Burnett et al was being devised, developed and tested, but which would provide a container which is useful under current USFDA guidelines and regulations for use in packaging food retailed to consumers. A comparatively difficult part of the present invention was devising ways and means for providing the circumferentially extending tear strip on the lid so that it could be easily and reliably torn-off by consumers provided with minimal and simple instructions.